Rapidly disintegrating detergent tablets and method of producing same



United States Patent 3,367,880 RAPHDLY DISINTEGRATING DETERGENT TABLETAND METHQD 0F PRODUCING SAME Russell R. Keast, Yardley, Pan, and AllanR. Wirth, Hopewell, and John S. Thompson, Princeton Junction, N.J.,assignors to FMC Corporation, New York, N.Y., a corporation of DelawareNo Drawing. Filed July 8, 1964, Ser. No. 381,216 Claims. (Cl. 252-438)ABSTRACT OF THE DISCLOSURE Process for producing strong but fastdissolving detergent tablets containing about 35 to 65% by weight ofsodium tripolyphosphate, 3 to about by weight of sodium silicate and 5to about 15% by weight of a water soluble, non-soap organic syntheticdetergent, wherein compacted sodium tripolyphosphate having a density offrom about 1.0 to about 1.25 g./ cc. and having a hydration time of lessthan about 3 minutes is utilized as the sodium tripolyphosphate in saidtablets.

This invention relates to the process for making heavyduty detergenttablets, and more specifically, to the production of detergent tabletswhich have an unusually high disintegration rate when placed in heatedwash water, but which are sufiiciently strong in the dry statetowithstand breakage.

Heavy-duty, built, synthetic detergent tablets have become increasinglypopular compared with liquid or powdered detergent compositions becauseof the more desirable handling characteristics which these tablets have.These tablets obviate the need for measuring cups used to dispense thepowdered or liquid detergents required in domestic washing machines.They also eliminate spillage and the problem of storing bulky detergentcontainers. In normal manufacture, the heavy-duty detergent formulationsare blended and pressed into tablets so that they have sufficientstrength to resist breakage in handling and use, but are capable ofdisintegration in an acceptable time in wash water under conditionsnormally found in domestic Washing machines.

In the makeup of detergent tablets, the principal ingredients employedare a phosphate builder such as sodium tripolyphosphate, ananti-redeposition agent such as sodium carboxymethylcellulose, ananionic or nonionic surfactant and an anti-corrosion agent such assodium silicate. In general these ingredients are mixed together to forma homogeneous dry mixture and are compressed in a mold to form a tablet.Of these ingredients, the surfactant and the phosphate builder are usedas the principal cleaning components. The anti-redeposition agent isemployed to prevent dirt from being redeposited on the washed clothes inthe wash water, and the anti-corrosion agent is added to prevent thealkaline detergent solution from attacking the metallic parts of thewashing machine. In addition, some formulas also contain inertingredients such as sodium sulfate which is added as an extender toobtain the desired bulk density in the pelletizing mix and to yield asmoother and more solid appearing tablet.

In the makeup of detergent tablets it has been customary to use low bulkdensity sodium tripolyphosphate, i.e. having a density of from about0.35 to about 0.6 g./cc. This is desirable because the extremely light,fluffy sodium tripolyphosphate can be compressed in the detergent tabletleaving a sufi'icient number of voids in the tablet to acceleratedisintegration of the resultant tablet in the wash Water.

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A problem that has arisen in the manufacture of detergent tablets is theinability to produce faster dissolving tablets without also diminishingthe strength of the dry tablets to withstand the shocks of packaging,handling, dispensing, and the like.

One approach to obtaining faster dissolution of the highly compressedtablets is the addition of additives such as CO generators, starch, orother inert materials which increase disintegration. However, many ofthese materials are expensive and are undesirable as ingredients in thedetergent tablet and therefore have not met with wide success. Othertechniques such as using low ram pressures during the pressing of thetablets have been proposed but have not been successful because theresultant tablet is not sufiiciently strong to withstand normal dryhandling.

As a result there is a need for a process for producing a detergenttablet whose strength in the dry state is comparable with other tabletspresently used in the art, but whose disintegration rate in the washwater used in conventional washing machines is substantially increasedover conventional tablets.

It is an object of the present invention to produce a detergent tablethaving acceptable dry strength but whose dissolving rate is extremelyhigh compared with conventional detergent tablets.

These and other objects will be apparent from .the followingdescription.

We have made a surprising discovery that detergent tablets which aremade up with a compacted sodium tripolyphosphate having a density offrom about 1.0 to about 1.25 g./ cc. and a hydration time of less thanabout three minutes, have an extremely fast dissolving rate and alsohave good dry strentghs sufficient to withstand normal handling andpackaging.

It is most surprising that a highly dense sodium tripolyphosphate yieldsa tablet having fast dissolving rates since only low bulk density sodiumtripolyphosphate (which is used to make up conventional detergenttablets) produces the large amounts of air voids within the tablet whichare considered mandatory to fast dissolving rates. The general beliefprevalent in the detergent industry has been that the more dense sodiumtripolyphosphate is not suitable for incorporation in detergent tabletsbecause its denseness would preclude a fast dissolving tablet.

A method for producing a compacted sodium tripolyphosphate producthaving a bulk density of from about 1.0 to about 1.2 and having ahydration rate of less than about three minutes is reported in ourco-pending application, Ser. No. 289,315, filed on June 20, 1963 in thenames Henry L. Marschall, et al. The term hydration rate refers to theperiod of time .required for the hydration of a given sample of sodiumtripolyphosphate and is carried out as follows:

One hundred mls. of water at 80 to 84 F. is placed in a clean, dry,l-pint, Wide-mouthed vacuum jar. A rotarydriven stirrer is inserted witha blade near the bottom of the jar and set at 400 r.p.m. Twenty-fivegrams of anhydrous sodium sulfate is then added to the vacuum jar. Whenthe anhydrous sodium sulfate is dissolved, the stirrer speed isdecreased to 200 r.p.m. and the solution temperature is adjusted to 80to 84 F. A -gram sample of the sodium tripolyphosphate to be tested isthen added evenly to the liquid over a period of 15 to 20 seconds. Whenall of the sodium tripolyphosphate has been added, a timer is begun. Thesurface of the mixture is observed and when all circular motion of thesurface stops, excepting the area directly adjacent to the stirrershaft, the end point has been reached and the timer is stopped. Theapproach of the end point is easily detectable because the sodiumtripolyphosphate-water mixture thickens a minute or so before the endpoint occurs and the mixture is so thick that the slurrying actionbecomes very sluggish. When the circulatory motion of the surface stops,this indicates that the end point has been reached. This does notinclude the small area directly adjacent to the stirrer shaft.

Conventional sodium tripolyphosphate normally has a hydration time offrom about 6 to 12 minutes while compacted sodium tripolyphosphatenormally has a hydration time of less than 3 minutes.

In the practice of this invention, the detergent formulation is made upas follows: The principal ingredient, the compacted sodiumtripolyphosphate, is measured into the detergent formulation in amountssuflicient to constitute from about 35 to about 65% by weight of thedetergent formulation. The preferred range of sodium tripolyphosphate isfrom about 50 to about 65% by weight with about 58% being the optimumamount.

The next added ingredient is the surface active agent (surfactant). Thesurfactant, which can be used in the makeup of the formulation, may beeither nonionic or anionic; certain cationic surfactants cannot beemployed because they are incompatible with the compacted sodiumtripolyphosphate. The surfactant is added to the mixture in amounts offrom about to about 15% by weight of the formulation. Ten percent byweight is generally considered optimum.

To the above mixture is added a sodium silicate having a Na O/SiO moleratio of from about 1:2 to about 1 :3.2 in amounts of from about 3% toabout 15% by weight of the formulation. Generally, about 7% of 81.5%active sodium silicate having a Na O/SiO mole ratio of 1:2 has beenfound to give good results. In general the optimum amounts of sodiumsilicate normally supply from about 3 to about 3.5 weight percent of SiOto the formulation.

The next added ingredient is sodium sulfate which constitutes theremaining major portion of the formulation. The sodium sulfate is aninert filler which is added to control the bulk density of the tabletingmixture and to improve the surface appearance of the tablets by givingthem a smoother and more compact appearance. In addition, there is alsoadded small amounts of auxiliary compounds such as sodiumcarboxymethyl-cellulose, generally in amounts of from about 0.2 to about1.5%, foam stabilizers such as lauroyl diethanolamide, tarnishinhibitors, fluorescent brighteners, perfumes, bacteriosta-ts, coloringmatter, etc. The resultant mixture thus formulated is uniformly mixedand pressed into tablets. The pressing is normally accomplished usingpressures of from about 175 to about 200 p.s.i. and the finished tablethas a bulk density of from about 0.8 to about 1.3 with about 1.02 beingpreferred. The newly formed tablets normally have strengths (whenpressed on edge) of from about 10 to about pounds. If the tablets aresuitably aged for at least 24 hours, they have a strength (when pressedon edge) of up to about 25 pounds. Desirably, these tablets havedissolving times of less than 120 seconds when placed in a conventionalwashing machine containing water at 120 F.

In the makeup of these detergent tablets, the compacted sodiumtripolyphosphate preferably has a bulk density of from about 1.0 toabout 1.25 g./cc. Further, the sodium tripolyphosphate should be made upof substantially all -16+100 mesh fraction and should contain no morethan about 20% 70 mesh.

The anionic surface active agents are useful in the present formulationsin amounts of from about 5% to about 15 by weight of the formulation.These anionic surface active agents are non-soap synthetic detergentsmade up of water-soluble salts or organic sulfuric reaction productshaving from about 8 to about 18 carbon atoms in the form of an alkyl oracyl radical with the molecular structure and containing sulfuric orsulfonic acid ester radicals. Typical examples of these anionic surfaceactive agents are sodium or potassium alkyl benzene sulfonates in whichthe alkyl group contains from about 8 to about 18 carbon atoms, e.g.sodium dodecyl benzene sulfonate, sodium tridecyl benzene sulfonate; thesodium and potassium alkyl glycerol ether sulfonates, including ethersof higher fatty alcohols derived from the reduction of coconut oils; thereaction products of higher fatty acids, e.g. coconut oil with sodium orpotassium isethionate; sodium or potassium alkyl sulfonates and sulfatesobtained by sulfonation or coconut or tallow fatty alcohols and mixturesof such alkyl sulfates; dialkyl esters of sodium or potassium salts ofsulfosuccinic acid; sodium and potassium salts of sulfated or sulfonatedmonoglycerides, e.g. those derived from coconut oil; sodium or potassiumsalts of higher fatty alcohol esters of sulfocarboxylic acids,- e.g.sodium salt of lauryl alcohol ester of sulfoacetic acid; and otheranionic agents set forth in US. Patent 2,486,921 issued to Byerly onNov. 1, 1949. If desired, the anionic surfactant can be added in theform of a dense, dry bead or as a flake admixed with sodium sulfate. Inthis latter case, the sodium sulfate constitutes a portion of the totalsodium sulfate used in making up the entire mixture.

The sodium silicate that is added to the mixture normally constitutesfrom about 3 to about 15% by weight of the detergent formulation. Themole ratio of Na O/ in the sodium silicate determines the degree ofalkalinity of this compound; as the ratio approaches 1:2 the sodiumsilicate becomes more alkaline. Ratios above 1:2, e.g. 1:1 are generallytoo alkaline and cause the wash water to reach pH levels which areunsafe for certain fibers. Ratios below 1:2.2, e.g. 1:4, dissolve tooslowly and are not effective.

The nonionic surface active agents useful in the present invention arenon-soap synthetic detergents made up of a water solubilizingpolyoxyethylene group in chemical combination with an organichydrophobic compound. Among the hydrophobic compounds which can be usedare polyoxypropylene, the reaction product of propylene oxide andethylene diamine, aliphatic alcohols, etc. Examples of nonionicsynthetic detergents useful in the present invention are, condensationproducts of 6 to 30 moles of ethylene oxide, and preferably 7 to 11moles, with 1 mole of an alkyl phenol containing 6 to 12 carbon atoms inthe alkyl group; condensation products of 6 to 30 moles of ethyleneoxide with 1 mole of an aliphatic straight or branch chained alcoholcontaining 8 to 18 carbon atoms; condensation products of ethylene oxideand the reaction product of propylene oxide and ethylene diamine; nonylphenol polyethoxy ethanol (commercially known as Triton N series);isooctyl phenol polyethoxy ethanol (commercially known as Triton Xseries). Another well known group of nonionic detergents is known underthe trade name of the Pluronic series. These compounds are the reactionproducts obtained by condensing ethylene oxide with a hydrophobic baseproduced by the condensation of propylene oxide with propylene glycol,and have molecular weights on the order of about 1800. The addition ofpolyoxyethylene radicals to the hydrophobic base increases the watersolubility of the nonionic detergent and concurrently increases the foaming properties of the detergent in aqueous solution in proportion to themole ratio of polyoxyethylene radicals to the hydrophobic base. Ingeneral, a surfactant which has a mole ratio of 7.5 moles of ethyleneoxide per mole of an alkyl phenol, e.g. nonylphenol, is low-foamingwhile one with a mole ratio of 10:1 foams moderately. The molecularweight of these nonionic synthetic detergents will range from as low as800 up to about 11,000.

Nonionic surfactants should be added to the present formulation inamounts of about 6% by weight of the total formulation or above in orderfor the surfactant to be completely effective. Amounts below about 6%reduce the cleaning action of the detergent and should be avoided.Amounts over 14% similarly should be avoided because the nonionicsurfactant tends to exude or oil out of the detergent formulation whenit is pressed into tablets. Within the range of 6% to 14%, the nonionicsurfactant gives effective washing action, and has been found to beeffective as a binder for the remainder of the detergent formulationwithout oiling out of the pressed tablet.

After the ingredients have been uniformly mixed together the resultingdry mixture should have a bulk density in the range of from about 0.4 toabout 0.85 g./cc. with the preferred bulk density being about 0.7 g./cc.Predetermined quantities of this mixture are then fed to a die andpressed at from 100 to about 350 psi. to yield a tablet havinga bulkdensity of about 1.02 g./cc. The resulting tablet has the followingformulation:

Percent by weight Sodium tripolyphosphate 35 to 65 Sodium silicate 3 to15 Sodium carboxyrnethylcellulose 0.2 to 1.5 Anionic or nonionic surfaceactive agent to 15 Sodium sulfate Balance In the procedure of tabletingthis detergent formulation, it has been found that small portions of thepressed mixture do not adhere to the dies, nor is there any cappingduring the pressing of this formulation. The term capping refers to theinternal horizontal separation of the tablet into two or more piecesbecause of the adherence of these pieces to each of the dies. Ingeneral, the use of standard dies is eminently. satisfactory withoutspecial provisions for rotation of the dies during the pressingoperation.

The resulting pressed tablets may be subjected, it de sired, to steamingin order to hydrate a surface layer of hydratable components, e.g.sodium tripolyphosphate and sodium sulfate. The steaming helps form afilm or layer of increased strength to help prevent fracturing of theproduct during normal handling. This steaming is helpful because thehydratable ingredients crystallize with such action that they create abinding force between adjacent particles. In addition, the applicationof moisture makes the surface more homogeneous, thereby increasing thesurface density and the cohesive force between the particles.

The following examples are given to illustrate the invention and are notdeemed to be limiting thereof:

EXAMPLE I Run A.--The following anionic detergent formulations weremixed in a Kitchen-Aid planetary mixer (Model 4-C, Hobart Manufacturing00., Troy, Ohio) for about 3 /2 minutes.

INGREDIENTS Sodium Tripolyphosphate Spray- Formula Bulk Hydration DriedDensity Time Weight, g. Bead, g.

(minutes) A spraydriod powdered product containing the followingproducts Percent by weight Sodium Tripolyphosphate 25 Anionic surfactant(sodium dodocylbenzone sulionate 100%) 26 Sodium Silicate (Na OISiOQmole ratio 1:2.4) 5 Moisture 8-11 Sodium carboxyrnethylcellulose 0.67Optical brightauers 0.2 Sodium sulfate a level of 1.4% by weight of thesodium tripolyphosphate. In Formula C, the fines level was 15% by weightof the sodium tripolyphosphate added. The tablets were then conditionedfor approximately 16 hours in sealed jars at ambient room temperaturebefore testing.

The tablets were tested for disintegration time by observing the time(in seconds) required for the tablets to be sufficiently reduced in sizeto allow escape from a /2 inch wire mesh cage suspended in a fixedposition in a transparent-sided Kenmore washer containing F. agitatingtap water. In addition, the crush strengths of the tablets were obtainedby measuring the force in pounds needed to crush the tablets when placedon edge. The tablets were not steamed after manufacture to increasetheir crush strength in order to obtain the best possiblereproducibility in test results. The results of the test are set forthin Tablet I.

Run B.By way of comparison, a detergent mixture (Formula D) was made upusing the same proportion of ingredients as set forth in Run A withsodium tripolyphosphate having about the same density as the compactedsodium tripolyphosphate except that it was not produced by the compactedprocedure and therefore retained a high hydration time of 7.4. When suchtablets were pressed into identical tablets by the same procedure as setforth in Run A, the crush strengths and disintegration times set forthin Table I were obtained.

1 Qompacted. 2 Reg. rotary kiln.

Pursuant to the requirements of the patent statutes, the principle ofthis invention has been explained and exemplified in a manner so that itcan be readily practiced by those skilled in the art, suchexemplification including what is considered to represent the bestembodiment of the invention. However, it should be clearly understoodthat, Within the scope of the appended claims, the invention may bepracticed by those skilled in the art, and having the benefit of thisdisclosure otherwise than as specifically described and exemplifiedherein.

What is claimed is:

1. In a process for producing strong, heavy-duty detergent tabletshaving a fast dissolving rate, wherein a formulation comprising fromabout 35% to about 65% by weight of sodium tripolyphosphate, from about3% to about 15% by weight of sodium silicate, and from about 5% to about15% by weight of a water-soluble non-soap organic synthetic detergentselected from the group consisting of anionic detergents selected fromthe group consisting of the sodium and potassium salts of alkylsulfates, alkyl sulfonates and alkyl aryl sulfonates having from about 8to about 18 carbon atoms in the alkyl group, and nonionic detergentsselected from the group consisting of the condensation products of about6 to about 30 moles of ethylene oxide with one mole of an alkyl alcoholwherein the alkyl group contains from about 8 to about 18 carbon atoms,and the condensation products of about 7 to about 11 moles of ethyleneoxide with one mole of an alkyl phenol wherein the alkyl group containsfrom about 6 to about 12 carbon atoms, is pressed into tablets having abulk density of about 1.0 g./cc., the improvement consisting essentiallyof making up said formulation with sodium tripolyphosphate having adensity of from about 1.0 g./ cc.

to about 1.25 g./cc. and a hydration time of less than about 3 minutes,said sodium tripolyphosphate being produced by passing an aqueous sodiumorthophosphate mixture through a heated zone to obtain an initial,particulate sodium tripolyphosphate having a bulk density of about 0.4to about 1.2 g./cc., compacting particles of said initial sodiumtripolyphosphate at temperatures below about 350 C. to form non-friable,compacted particles and grinding said compacted particles into granular,sodium tripolyphosphate, whereby the dissolving rate of said tablets isincreased without diminishing the dry strength of said tablets.

2. The process of claim 1 in which the formulation contains from about50% to about 65% by weight of sodium tripolyphosphate.

3. The process of claim 1 in which the watersoluble non-soap organicsynthetic detergent is sodium dodecylbenzene sulfonate.

4. In a process for producing strong, heavy-duty detergent tabletshaving a fast dissolving rate, wherein a formulation comprising about58% by weight of sodium tripolyphosphate, about 5% by weight of sodiumsilicate. from about 5% to about by weight of a watersoluble non-soaporganic synthetic detergent selected from the group consisting ofanionic detergents selected from the group consisting of the sodium andpotassium salts of alkyl sulfates, alkyl sulfonates and alkyl arylsulfonates having from about 8 to about 18 carbon atoms in the alkylgroup, and nonionic detergents selected from the group consisting of thecondensation products of about 6 to about 30 moles of ethylene oxidewith one mole of an alkyl alcohol wherein the alkyl group contains fromabout 8 to about 18 carbon atoms, and the condensation products of about7 to about 11 moles of ethylene oxide with one mole of an alkyl phenolwherein the alkyl group contains from about 6 to about 12 carbon atoms,from about 0.2% to about 1.5% by weight of sodium carboxymethylcelluloseand sodium sulfate, is pressed into tablets having a bulk density ofabout 1.0 g./cc., the improvement consisting essentially of making upsaid formulation with sodium tripolyphosphate having a density of fromabout 1.0 g./cc. to about 1.25 g./cc. and a hydration time of less thanabout 3 minutes, said sodium tripolyphosphate being produced by passingan aqueous sodium orthophosphate mixture through a heated zone to obtainan initial, particulate sodium tripolyphosphate having a bulk density ofabout 0.4 to about 1.2 g./cc., compacting particles of said initialsodium tripolyphosphate at temperatures below about 350 C. to

form non-friable, compacted particles and grinding said compactedparticles into granular, sodium tripolyphosphate, whereby the dissolvingrate of said tablets is increased without diminishing the dry strengthof said tablets.

5. A novel heavy-duty detergent tablet having a fast dissolving rateconsisting essentially of from about 35% to about by weight of sodiumtripolyphosphate having a density of from about 1.0 g./cc. to about 1.25g./cc. and a hydration time of less than about 3 minutes, said sodiumtripolyphosphate being produced by passing an aqueous sodiumorthophosphate mixture through a heated zone to obtain an initial,particulate sodium tripolyphosphate having a bulk density of about 0.4to about 1.2 g./cc., compacting particles of said initial sodiumtripolyphosphate at temperatures below about 350 C. to form non-friable,compacted particles and grinding said compacted particles into granular,sodium tripolyphosphate, from about 3% to about 15% by weight of sodiumsilicate, from about 5% to about 15% by weight of a water-solublenon-soap organic synthetic detergent selected from the group consistingof anionic detergents selected from the group consisting of the sodiumand potassium salts of alkyl sulfates, alkyl sulfonates and alkyl arylsulfonates having from about 8 to about 18 carbon atoms in the alkylgroup, and nonionic detergents selected from the group consisting of thecondensation products of about 6 to about 30 moles of ethylene oxidewith one mole of an alkyl alcohol wherein the alkyl group contains fromabout 8 to about 18 carbon atoms, and the condensation products of about7 to about 11 moles of ethylene oxide with one mole of an alkyl phenolwherein the alkyl group contains from about 6 to about 12 carbon atoms,from about 0.2% to about 1.5% b weight of sodium carboxymethylcellulose,the balance of the formulation being made up of sodium sulfate, saiddetergent tablets having a bulk density of about 1.0 g./cc.

References Cited UNITED STATES PATENTS 3,081,267 3/1963 Laskey 252FOREIGN PATENTS 652,764 11/1962 Canada.

LEON D. ROSDOL, Primary Examiner.

B. BETTIS, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,367,880 February 6, 1968 Russell R. Keast et a1.

It is certified that error appears in the above identified patent andthat said Letters Patent are hereby corrected as showm below:

Column line 34, "strentghs" should read strengths Column 3, l1ne 71,"with" should read within Column 4, l1ne 31, "1:2.2" should read H 1:3.2Column 6, line 17 "Tablet" should read Table Signed and sealed this 23rdday of September 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents WILLIAM E. SCHUYLER, JR.

